Red Hot Chili Peppers with Guns N Roses opening
This was a club gig at UCLA. The Peppers at that time were the annointed next-big-thing in the LA club scene, and a great band to catch in a club setting. GNR was more of an unknown band and did not get along well with the crowd (people I know who went to that gig said that GNR played poorly and Axel Rose spent way too much time cussing out the audience), and apparently got booed off the stage.

Miles Davis and The Grateful Dead
The Fillmore in San Francisco in the 60s and 70s was legendary for some of its adventurous concert pairings. I've see the poster for the Miles/Dead concert, and can only imagine how that evening must have sounded! I have no idea if the Dead were backing up for Miles or if he brought his own band along. But, it would not surprise me at all if Miles actually played with the Dead, because this was during Miles' In A Silent Way/B*tches Brew/Jack Johnson phase. A lot of extended jam sessions in those pieces, and the Dead were one of the great jam bands of all time.